akinsanya, olawale - The Federal University of Agriculture, Abeokuta

SOIL CHEMICAL PROPERTIES IN RELATION TO LEVELS OF SOIL PHYSICAL
DEGRADATION IN ALABATA,
SOUTHWESTERN NIGERIA·
AKINSANYA, OLAWALE
(01/0080)
A PROJECT SUBMITTED TO THE POSTGRADUATE SCHOOL, UNIVERSITY OF
AGRICULTURE, ABEOKUTA IN PARTIAL FULFILMENT OF THE AWARD OF POST·
GRADUATE DIPLOMA IN SOIL MANAGEMENT AND LAND USE PLANNING
DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL
MECHANIZATION
COLLEGE OF PLANT SCIENCE AND CROP PRODUCTION
UNIVERSITY OF AGRICULTURE
ABEOKUTA,
NIGERIA

DECLARA liON
I hereby declare that this dissertation
has been written by me and is a record of my own research work.
It has not been presented in any previous application for a higher degree of this or any other University.
All citations and sources of information are clearly acknowledged
by means of references.
Akinsanya,
Olawale.
Date ~ .

his is to certify that this work, carried out by AKINSANYA, OLAWALE Department of Soil Science
nd Agricultural Mechanization, University of Agriculture, Abeokuta, Nigeria under the supervision
tof Dr. F.K. Salako meet the regulation governing the award of the degree of Post-Graduate
,Diploma of the University of Agriculture. Abeokuta, Nigeria and is approved for its contribution to
scientific knOWledgeand literary presentation.
B. Agric., M.Sc. (Nig.), Ph.D. (Ibadan)
Senior Lecturer in Soil Physics/Soil Conservation
Dr. F. K. Salako
Acting Head
Department of Soil Science and Agricultural Mechanisation
iii

ABSTRACT
This study was carried out in 2002 at the University of Agriculture, Alabata, near Abeokuta,
southwestern Nigeria ... It was part of two experiments established in 2001 on two previously
degraded sites. Soil degradation processes were by soil erosion in Experiment 1 and by
mechanization in Experiment 2. 80th experiments were randomized complete block designs with 3
replications in Experiment 1 and 4 replications in Experiment 2. Treatments in Experiment 1 were
levels of soil degradation, classified as fairly, moderately and severely degraded while flat
(mechanical) and mound (manual) tillage practices were compared in Experiment
2. Upland rice
(ITA 150, ITA 321, WAS 189 and WAS 450) was the test crop in Experiment 1 and maize (Acr 86-
TZESRW) was the test crop in Experiment 2. Clay in the fairly degraded soil was significantly higher
than in the moderately degraded soil while the highest sand content was observed in the severely
degraded soil. Although the soils were not chemically degraded, the coefficients of variation of soil
chemical properties was up to 54% depending on the parameter. The wide variations among levels
of soil degradation suggested that the fertility management of the soil would be difficult. Soil
chemical properties between flat and manual tillage were not significantly different, and did not vary
as much as in Experiment 1, suggesting that the previous mechanical and manual tillage practices
had no significant residual effects on the soil chemical properties. This study showed that physical
processes of soil degradation
had varying effects on soil chemical properties, with soil erosion
causing higher variation than tillage practices.
Also, cultivation of different rice varieties influenced
the variability observed.

DEDICATION
iCated to God Almighty, who forever shall be and my children Akinwole,

ACKNOWLEDEMENT
The Lord is good all the time in my life to make it possible for me to successfully complete this
programme. So, I am very grateful to HIM for his guidance, provision and protection from my childhood
and to this day.
I am grateful to my supervisor
Dr. F.K. Salako for his thorough guidance, aids and support,
morally 'and financially, throughout this project work. May God in his infinite mercy continue to be your
source of power.
I further wish to show my gratitude to all the lecturers in Department
of Soil Science and
Agricultural Mechanization of the University for their encouragement and support, mosUy in the
knowledge impacted on me.
My special gratitude goes to my father Mr. 1.0. Akinsanya (JP) and Evang. C.A. Akinsanya who
have been my source of encouragement
morally and financially.
I want to also appreciate my wife for her moral support for me during the period of this course
of study.
My sincere gratitude also goes to my younger brother Akintunde Oluwaseyi Akinsanya for his
moral and financial assistance.
I also show my special gratitude to Adeyemo 'Femi and Opabode 'Sina for their numerous
support for me during the period of this course.

TABLE OF CONTENTS
TITLE PAGE
DECLARATION
CERTIFiCATION
i
ii
iii
ABSTRACT " ,iv
DEDiCATION , v
ACKNOWLEDGEMENT
vi
TABLE OF CONTENTS vii-viii
CHAPTER ONE
1.0 INTRODUCTION 1-2
CHAPTER TWO
2.0 LITERATURE REViEW J
2.1 SOIL DEGRADATION AND REHABILITATION 3 - 4
2.2 SOIL MANAGEMENT IN THE TROPICS 5 - 6
2.3 CEREAL PRODUCTION IN THE TROPICS 6
CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 SITES 7 - 8
3.2 SOIL SAMPLING 9
3.3 LABORATORY ANALYSIS 10 -12
3.4 DATA ANALYSIS 12

CHAPTER FOUR
4.0 RESULT
·~·t·. RICE PLOT 13·20
CHAPTER FIVE
5.0 DISCUSSiON 30 - 31
REFERENCES 33-37
.:·,~OIX 38 -44
--

INTRODUCTION
Nutrient depletion of weakly structured tropical soils through long-term cultivation without
supplementary addition of nutrients and inappropriate tillage practices are major problems on arable
land in West Africa (Kirchhof and Salako, 2000). In the process of degradation, the capacity of the soil to
produce enough food to meet the expectation of farmers reduces.
Rice and maize are part of the major cereal crops that tolerate most warm conditions as found
in southwestern Nigeria. The crops are grown for their grains on a wide variety of soils in the tropics,
ranging from sand to heavy clay. These grain crops do not sustain their yields after prolonged cultivation
on a piece of land (Lal, 1997a, 1997b). Due to pressure on available arable land, farmers use land for
continuous cultivation without necessary inputs for sustainable production. So in the tropics, particularly
Africa, it is important to evaluate changes in soil properties under prolonged or continuous cultivation of
land.
The fertility of the soil is controlled by its pH, exchangeable bases and cation exchangeable capacity
(CEC). These affect the retention of plant nutrients that are available to the plant, thereby reducing crop
nutrient uptake and performance. Most tropical soils are highly weathered, acidic and very low in cation
exchangeable capacity, hence reducing the exchangeable cations in the soil (Sanchez, 1976 and Igwe
et al,1995). Low fertility of the soil is caused by prolonged cultivation without nutrient replenishment. The
soils contain mostly the 1:1 non-expanding kaolinite clay minerals, aluminum and iron oxides. These are
described as low activity clay (LAC) by Harris et al,1996 and Lal, 1985.Thus, the soils hold water and
nutrients marginally, and are highly susceptible to water erosion. After two or three years of cultivation,
soil productivity steeply declines.

...
-Soil chemical properties of an Alfisol at different levels of degradation under rice cultivation
,~ohemical
....... -
-: ;.
properties of a previously cultivated soil in relation to mechanical and manual tillage using

CHAPTER TWO
LITERATURE REVIEW
2.1 SOIL DEGRADATION AND REHABILITATION
Soil degradation processes are phenomena that cause a decrease in the quality of soils and
can be divided into three interactive groups: physical, chemical and biological degradation. However
the primary soil degradative process is physical (Moorman and Greenland, 1980). The most
common land degradation is due to improper land management that can cause soil erosion. Most
farmers do not use proper soil conservation and management practices.
Soil degradation decreases the potential capability of soil to produce goods and services. It could
have occurred due to continuous cultivation, but may also occur over a short period if soils are not
properly managed, especially with high rainfall erosivity, which is characteristic of the tropics.
EI-Swaify (1998) observed processes of soil degradation to include soil erosion and nutrient
depletion, which are accelerated by demographic pressure. However, the definition of a degraded
land is elusive because there are various levels of soil degradation and different satisfactory levels
of soil rehabilitation depending on intending land use after the rehabilitation program (Barrow, 1991;
Harris et aI., 1996). Soil physical degradation in tropical Alfisol occurs during initial forest clearing
before cultivation commences and it is often due to raindrop impact on the exposed soils (Lal,
1976). Mechanical, human and animal traffic can compact this soil, reducing its capacity to produce
crops (Ghuman and Lal, 1991a; Ghuman et ai, 1991; Lal, 1992). Cultivated lands may not be
degraded depending on the soil management practices adopted by farmer. In this respect, it has to
be emphasized that a previously cultivated land may not be degraded because the productive
capacity of the land for a suitable crop may still be adequate.
3

Productivity of severely degraded soils may not be restored on a human time scale
Johnsonand Bradshaw, 1979), especially in highly populated countries where production and profit
goalsprevail over environmental concern. In southwestern Nigeria, farmers cultivate sites that are
predisposedto erosion by steep slopes and they would not adopt soil conservation measures if it is
expensiveor n~t in tune with their cultural practices (Ekanade, 1997). Such practices render soils
severely degraded and one consequence of this is the transformation
of forests to derived
savannah.Plinthite or its related forms are hardened and cemented after exposure by soil erosion in
thetropics, resulting in barren land (Eswaran et ai, 1990) or a derived savanna in once forested
agroecological zone like some parts of southwestern Nigeria.
Degraded soils are structure less and fragile in nature (Oldeman, 1990; 1994). They are
exposedto erosion by water and may have their topsoil washed away. Greenland (1977) found that
thestructures of topsoil are more prone to deterioration under raindrop impact so it should be given
muchattention. In the soil, root growth is either slowed down or prevented depending on the level of
compaction. Suwardjo et al (1991) reported that land degradation is a serious problem in upland
agriculture. It is caused by such activities such as shifting cultivation, erosion, improper land use,
land clearing, etc. Accelerated erosion is also a major factor responsible for soil fertility depletion
and a decline in productivity of soils in the tropics (Mohammad and Gumbs, 1982).
Land restoration is the process by which a degraded land is returned to its original state (Harris et
ai, 1996). Natural fallow has been an age-long practice for restoration of soil productivity in the
tropics (Aweto, 1981). Whether or not true rehabilitation can ever be fully achieved is a vexed
q~~stion because natural systems may change with time and the scale the system is examined will
affect observations.

2.2 SOIL MANAGEMENT IN THE TROPICS
Soil productivity encompasses biological, physical and chemical fertility. Farmers in the tropics were
able to judge soils productivity based on indigenous knowledge gathered from cropping systems and
crop yields (Ishida and Tian, 2001). Often, it is easier to improve soil chemical fertility through addition of
organic and inorganic nutrients than to improve physical and biological fertility. However, use of
inorganic fertilizers is costly for resource-poor farmers in the tropics Inoganic fertilizer recommendations
in the tropics require caution because some fertilizers degrade the soil through acidification, although
the right use of inorganic fertilizers usually boost crop production substantially (Juo et aI., 1995a; 1995).
Organic manure is equivalent to chemical fertilizer in terms of soil improvement (Tanaka, 1975;Yamane,
1974). Cooke (1982) reported that fresh poultry dropping contained twice as much phosphorus as some
inorganic fertilizers
Manure increases organic matter content, water content and water movement in soil. It also results in
reducing soil bulk density thereby reducing compaction and increasing crop-rooting depth.
Soil physical properties can be improved or sustained using management practices, which include
manual clearing, residue mulch, use of organic manure, cover cropping and alley cropping (Akobundu,
1980; Tian and Kang, 1998; Kang et m. 1999; Kirchhof and Salako, 2000). These systems are
potentially sustainable. Also, yields can be improved by cultivating land with appropriate cropping
intensities (Kang et m, 1990).
In spite of the improvement of soil properties by herbaceous legumes such as Mucuna and
Crotalaria. farmers in the tropics prefer gowing fopd legumes such as cowpea (Kirchholf and Salako,
2000), primarily for economic gains. For instance, Mucuna cover cropping has been adopted in recent
years by farmers in southern Benin republic, (Manyong et m, 1996), not because of soil conservation
5

and fertility management consideration only, but because of reduced labour for weed control.
Conservation @age, which includes minimum tillage or no tillage with incorporation or residue
mulch/cover cropping is an aspect of soil management that can guarantee sustainable crop production
in the tropics (Lal, 1997a; 1997b). Previously cultivated lands may not necessarily be degraded if
sustainable crop production practices were adopted.
2.3. CEREAL PRODUCTION IN THE TROPICS
Maize (Zea mays, L.) thrives well in the tropics but its production can be boosted further by provision of
nutrients and appropriate soil management practices in a given environment. According to David and
Adam (1985), maize is one of the world most important cereal crops. Maize is usually grown on wellstructured
soils of intermediate texture (sandy loams to loams). Maize can be cultivated by conventional
tillage, minimum tillage or zero tillage. Farmers are intensively using land for continuous cultivation with
none or few input. So in the tropics, particularly Africa, it is important to evaluate the changes in soil
properties as a result of continuous cultivation of the land.
Rice (Oryza'sativa) is very important as a staple food and an economic crop in many countries. It is both
indigenous and exotic crop in Africa. Rice production is concentrated in Asia where more than 90% of
the world supply is concentrated (FAO, 1981). Farmers cultivate rice in Africa mostly by depending on
the natural rise and fall of streams and shallows swamps to flood the crop, and in the upland on rainfall
to provide with ad~quate moisture.

CHAPTER THREE
MATERIALS AND METHODS
3.1. SITE
The study was conducted under an experiment, which was established in 2001 (Salako F.K,
personal communication) at the University of Agriculture, Alabata road, Abeokuta (Latitude 7.1 North
and Longitude 3.3 East), southwestern Nigeria. Annual Rainfall is averagely 1200 mm and it has a
bimodal distribution. The vegetation is a derived savannah and soil type is an Alfisol. Two
experimental sites were used for the research work~
3.1.1. EXPERIMENT 1: RICE PLOT
This site was under about 3 years of fallow by 2001, after being abandoned due to low productivity
(Salako F. K., personal
communication).lt was at various levels of physical degradation and this
was visible from the phases of soil eroson indicated by exposure of stones, gravel and boulders
(Fig. 1). Gravel concentration is usually high in the B horizons of these Alfisols (Salako et aI., 1999)
and could only have been exposed at the surface by erosion of the topsoil.
Columns were
demarcated into three levels depending on visually observed gravel concentration, although
laboratory tests were used to further support the divisions.
Three levels of soil degradation by soil erosion process were classified along the slope.
These were fairly degraded, moderately degraded and severely degraded.
Subsequent agronomic
yield showed that this delineation was right.
A randomized complete block design was used. Plot
size was 4 x 3 m. Four rice varieties were grown under poultry and NPK (20: 10: 10) application in
2001 and 2002. The rice varieties were ITA 150, ITA 321, WAB189 B-B-B-8-HB and

REPl
~
>.-
.!:: 3:
co 0
LL .0
IREPl
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WAS450. Poultry manure was applied at 15 t ha- 1 and fertilizer N was at 80 kg N ha- 1 . Crop
growth and yield for ITA 150 and WAS 189 grown on this site in 2001 were described by Uthman
(2002). The variety, WAS 189 yielded 1.3 Uha while ITA 150 yielded 0.6 Uha paddy rice.
The site was located on the lower part of a slope that had been mechanically cultivated for about
three, years, prior to this study.
Also, adjacent to this strip of mechanically cultivated strip, was a
strip of manually tilled plots with mound. The mechanically cultivated soil was more compact than
the manually tilled plot. Thus, the present experiment was imposed on these two existing land uses
to have flat tillage with hoe on the mechanically tilled strip and re-built mounds on the mounded strip
in 2001. The site was demarcated into 40 plots, each of which measured 5 m x 4 m. Randomized
block design was used with 4 replicates. The fertility management included the application of poultry
manure that was applied at the rate of 15 t ha- 1 and NPK (20:10:~was applied t have 80 kg N ha- 1 .
Mucuna pruriens was planted as a cover crop. Preparation of the land for the second year of
cropping commenced in April 2002. Maize (Acr86TZESRW) was also planted in April 2002, at a
spacing of 100 cm x 25 em.
Soil samples used for this study were collected from the topsoil (0-15cm) using soil auger for the 72
plots on the rice field and the 40 plots on the maize field. The sampling was done after harvesting
rice and maize in 2002.
The samples were air-dried for 72 hours and sieved using less than 2mm
sieve size for particle size and cation analyses. Samples less 0.05 mm were used for organic
carbon determination.

3.3. LABORATORY ANALYSIS
3.3.1. SOIL PARTICLE SIZE ANAL YSIS
This was done using the Bouyoucos (Hydrometer) method, which relies on the effects of particle size on
the differential settling velocities within a water column. Fifty grammes of air-dried soil (were placed into
a 400ml beaker. The soil was saturated with distilled water with 10 ml of 10% Calgon solution added
and allowed to stand for 10 minutes.
The Calgon treated soil was transferred into the dispersing cup and made to the mark on the cup with
distilled water 100ml). The suspension was stirred for 2 minutes with electric high-speed stirrer before it
was transferred into a graduated measuring cylinder and remaining soil was rinsed into the cylinder with
distilled water. The solution was made up to 1000 ml and stirred within the cylinder. Hydrometer was
then inserted into the suspension. At 40 seconds hydrometer reading of the suspensions was made.
After two hours, both hydrometer readings were taken again. Room temperatures were recorded during
each reading. The readings taken at 40seconds were assigned to the sand content and the readings at
two hours assigned to clay content of the original suspension. The percentage silt was calculated as a
difference between 100 and sum of sand and clay.
3.3.2. SOIL pH
Soil pH was determined in soil: water ratio of 1:2 (Henderson and Lalende, 1993). A 10-g
sample was placed in a 50 ml plastic shaking bottle. Then 20 ml of distilled water was added to each
sample. The bottles containing the samples were shaken for 30 min. with an electric shaker and were
allowed to stand for about 15 min. The electrode of the pH meter was immersed in each of the settled
suspension and the values of the soil pH were determined from the meter.
10

3.3.3. SOIL ORGANIC CARBON
Organic carbon was determined using a procedure described by Walkey and Black (1934)
and modified by Allison (1965).
One gram of air-dried soil lesser than 0.5 mm diameter was
weighed into ~ach 500 ml flask from each sample. Then 10 ml of 1N potassium dichromate
(K2Cr207)was added into the flask and concentrated sulphuric acid was added to the solution. The
solution was allowed to cool for 20 min. Then 100 ml of distilled water was added and followed by 5
drops of ferroin indicator. The solution was then titrated with 0.5M ferrous sulphates to get the end
point. A blank titration was also carried out.
The organic carbon value was calculated as:
% Organic carbon = (a-b) x 0.5 xO.003x 100 x f.
a = ml of Fe2S04 in blank solution
b = ml of Fe2S04 in soil solution
f = Titration factor (77% or 1.33)
Percentage of soil organic matter was calculated by multiplying carbon percentage with
3.3.4. EXCHANGEABLE BASES IN SOIL
The soil samples (5g each) were extracted with an excess of 1M NH40Ac (Ammonium
acetate) solution such that the maximum exchange occurred between the NH4 and the cations
originally occupying exchange sites on the soil surface. The amounts of exchangeable sodium,
potassium, calcium and magnesium in the extracts were determined by flame photometry (Na and
K) and by atomic absorption spectrometry (Ca and Mg)
11

3.3.5. EXTRACTABLE PHOSPHORUS
Phosphorus was extracted using Bray-1 extractant. This was done by weighing 5 g of airdried
soil into extraction cups into which 30ml of Bray-1 extractant solution was added. Treated
samples were transferred into the auto analyzer cups to read P content of soil
3.4. DATA ANALYSIS
The results of the chemical analysis were analyzed using the generalized linear model (SAS, 1988)
and means were separated using least significant difference (LSD) at P=O.05.

CHAPTER
FOUR
RESULTS
4.1. RICE CULTIVATION AT DIFFERENT LEVELS OF SOIL DEGRADATION
4.1.1. PARTICLE SIZE DISTRIBUTION
The sand contents in the severely and moderately degraded soils (Fig. 1) were not significantly
different (Table 1). However both had significantly higher sand content than the fairly degraded soil. For
the silt content, the fairly degraded strip had the highest amount of silt whereas the severely degraded
strip had the least silt content. There was a significant difference in clay contents of the fairly degraded
and moderately degraded levels. Silt and clay varied more than sand under rice cultivation with the
coefficient of variation for sand being less than 5% while up to 80% was observed for clay (Table 2).
4.1. 2. SOIL ACIDITY, ORGANIC MATTER AND EXTRACTABLE PHOSPHORUS
The soils were acidic with significant differences in pH between the severely degraded site and
other levels of degradation (Table 3). Exchangeable acidity was, however similar among the various
levels of soil degradation while organic matter content in the moderately degraded stirp was significantly
lower than those observed in the severely degraded strips. Phosphorus in the moderately degraded site
was significantly higher than P contents of the fairly degraded and severely degraded strips (Table 3).
The coefficients of variation were less than 10% for pH. However coefficient of variation were generally
higher than 10% in organic matter and good level of fluctuation in the variability of extractable P
(Table 4).

TABLE 1: EFFECT OF DEGRADATION ON SOIL PARTICLE SIZE ANALYSIS.
Particle size distribution (glkg)
Level of degradation
Sand
Silt
Clay
Fairly degraded
800
193
27

TABLE 2:
VARIATION IN PARTICLE SIZE DISTRIBUTION UNDER VARIOUS RICE VARIETIES
AT DIFFERENT LEVLES OF DEGRADATION
Coefficients of variation (%)
Level of degradation Sand Silt Clay
ITA 150
Fairly degraded 1 4 4
Moderately degraded 4 19 1
Severely degraded 2 17 2
ITA 321
Fairly degraded 4 17 1
Moderately degraded 1 5
Severely degraded 2 10 31
WAB 189
Fairly degraded 2 15 70
Moderately degraded 3 20 80
Severely degraded 2 13
WAB 450
Fairly degraded 3 10 29
Moderately degraded 10 9
Severely degraded

TABLE 3: SURFACE SOIL (O-15CM) ACIDITY, ORGANIC MAnER
AND EXTRACTABLE P ON
THE DEGRADED ALFISOL
Soil chemical properties
Organic
Extractable
Level of degradation pH (1:1 H2O) H+ matter (%) P (mg/kg)
Fairly degraded 5.66 0.086 5.39 2.14
Moderately degraded 5.63 0.084 3.67 2.41
Severely degraded 5.58 0.082 4.42 2.11
LSD (0.05) 0.13 NS 1.19 0.17

TABLE 4: VARIATION IN SOIL ACIDITY, ORGANIC MATTER CONTENT AND EXTRACTABLE P
DISTRIBUTION UNDER VARIOUS RICE VARIETIES AT DIFFERENT LEVLES OF
DEGRADATION
Coefficients of variation (%)
Organic
Level of degradation pH matter Extractable P
ITA 150
Fairly degraded 2.87 12.80 14.63
Moderately degraded 2.68 34.32 15.27
Severely degraded 2.22 53.54 6.38
ITA 321
Fairly degraded 0.09 31.09 4.46
Moderately de'graded 1.90 52.08 25.28
Severely degraded 2.22 48.16 3.93
WAB 189
Fairly degraded 4.18 30.36 9.34
Moderately degraded 3.07 18.92 14.68
Severely degraded 0.69 18.27 2.70
WAB 450
Fairly degraded 1.25 44.68 10.9
Moderately degraded 5.48 31.90 1.72
Severely degraded
- Not determined
17

4.1.3: SOfL CAnONS CONTENT
Potassium (K) content reveals no significant difference in all the levels of degradation, while
Exchangeable Calcium (Ca) in the moderately degraded soil was significantly different from the severely
degraded fraction, which is higher in quantity. Exchangeable Magnesium (Mg) content was not
significantly' different between the various degradation levels. The soil sodium (Na) content for fairly
degraded fraction was
significantly higher to severely degraded soil (Table 5). Crop nutrients
requirement from sandy soils benefit more from regular and generous application of organic and
inorganic fertilizer than organic matter stock of the soil because of erosion. The depletion of fine
materials by erosion may also be the cause of the low level of organic matter.
The higher cations concentration in the fairly degraded soil suggests that there was less
leaching or erosion of nutrients from the surface soil compared to the moderately and severely
degraded site. The Sodium (Na) content was however very low that even the relatively high content
would not cause salinity problem. The acidic pH level has already indicated this.
The Coefficients of Variation (CV) suggest that soil management for replenishment of organic
matter and phosphorus, Calcium (Ca), Magnesium (Mg) and Potassium (K) will be very difficult for rice
as these did not just vary with level of soil degradation, but also with the rice variety cultivated.

TABLE 5: SURFACE SOIL (0-15CM) CATION CONTENT IN THE VARIOUS LEVELS OF
DEGRADATION ON THE DEGRADED ALFISOL.
Mg
0.67

TABLE 6: VARIATION IN RICE VARIETIES AND SOIL EXCHANGEABLE CATIONS AT
DIFFERENT LEVLES OF SOIL DEGRADATION
Coefficients of variation (%)
Level of degradation K Ca Mg Na
ITA 150
Fairly degraded 6.67 19.16 32.00 19.17
Moderately degraded 12.5 16.67 26.00 19.48
Severely degraded 54.17 15.04 40.00 21.65
ITA 321
Fairly degraded 5.00 20.75 12.7 55.00
Moderately degraded 6.36 40.75 1.20 42.86
Severely degraded 10.51 23.87 16.30 4.55
WAB 189
Fairly degraded 59.26 18.94 36.51 20.83
Moderately degraded 10.0 20.69 33.33 18.07
Severely degraded 0.00 15.67 10.0 23.10
WAB 450
Fairly degraded 17.08 28.49 16.44 78.26
Moderately degraded 9.52 16.00 8.47 12.00
.Severely degraded
-Not determined

4.2. MAIZE CULTIVATION IN RELATION TO TILLAGE ON A PREVIOUSLY DEGRADED
ALFISOL
4.2.1. PARTICLE SIZE DISTRIBUTION
There was no significant difference in the soil particle fractions under the two tillage practices for
maize cultivation in 2002 (Table 7). Though the dominance of sand was prominent as part of the soil
forming processes (e.g. eluviations), soil erosion causing removal of finer particles also contributed
to it. The low content of clay and silt showed high depletion of fine materials by soil erosion. With
this low clay content the field would be low in cation exchange capacity as well as structural stability.
It would however appear that surface soils of alfisols in southwestern Nigeria are generally high in
sand content (Salako and Hauser, 2001).
There was also significant difference in the pH of the two tillage practices. The pH of the site being
weakly acidic pointed out that the experimental site is low in cations (table 8). There was no
significant difference in the organic matter content of the soils of the two tillage practices. The low
pH and organic matter were probably due to the continuous cropping of the soils and insufficient
recycling of plant and nutrients (Okeleye and Adetunji, 1998).
The chemical degradation has depleted much of the topsoil's cations and the soil is being rendered
. acidic. The organic matter content was low, which agrees with Davies et m, (1993) description of
organic matter levels of arable sandy soils. According to David et m (1989), organic matter of
tropical soils is dynamic due to climatic changes, which cause forming, and disruption of soil
aggregates.

TABLE 7: PARTICLE SIZE DISTRIBUTION UNDER DIFFERENT TILLAGE PRACTICES AND
MAIZE CULTIVATION AFTER LAND DEGRADATION IN ALABATA, ABEOKUTA,
SOUTHWESTERN NIGERIA
Particle size distribution (glkg)
Tillage Sand Silt Clay
Flat 871 118 11
Mound 774 114 12
LSD (0.05) NS NS NS
NS = No significant difference

TABLE 8: SOIL ACIDITY, ORGANIC MAnER
CONTENT AND AVAILABLE P UNDER DIFFERENT
TILLAGE PRACTICE.
Tillage pH Organic matter Extractable P
Flat till 5.72 3.66 2.96
Mound 5.67 3.73 2.72
LSD (0.05) 0.041 NS
,
NS

There was no significant difference in the soil particle size analysis for all the treatments of fertility
management (table 9). Particle size distribution of the surface soil was similar for the three fertility
management treatments.
The textural analysis of the soils revealed that the soil was sandy loam with pH of 5.69 with no
significant difference in the treatments showing that the soil is slighUy acidic (table 10). These
chemical properties indicate the inherent low fertility status of the soil due to the presence of low
activity clay (Lal, 1992). There is no significant difference in the low organic matter content of the
soils. The predominance of sand and gravel in particle size distribution and low organic carbon
showed that the soil structure would be weak. The available Phosphorus content shows no
significant difference, though it is very low.

Particle size analysis (g/Kg)
Fertility management Sand Silt Clay
None 871 119 10
Poultry 874 114 12
Mucuna 874 114 12
LSD (0.05) NS NS NS

TABLE 10: INTERACTION OF FERTILITY MANAGEMENT WITH SOIL ACIDITY, ORGANIC MATTER
AND AVAILABLE
P
Fertility management pH Organic matter Extractable P
None 5.69 3.72 2.85
Poultry 5.69 3.70 2.95
Mucuna 5.96 3.70 2.62
LSD (O.OS) NS NS NS

The coefficient of variation were less than 10% in all the parameters puts into consideration
except in clay content of the soil having high coefficient of variability which was as high as 53%
(Table 11). This level of variability in clay indicates that soil management for the replenishment of
the exchangeable cations and other soil inherent properties for productivity will be very difficult
despite the level of tillage adopted.

TILLAGE AND FERTILITY MANAGEMENT.
Coefficients of variation (%)
Fertility management Sand Silt Clay
Flat
N

SOIL ACIDITY, ORGANIC MAnER
AND AVAILABLE P
Coefficients o~variation (%)
Fertility management PH Organic matter Extractable P
Flat
None 0.88 0.54 1.64
Poultry 0.35 1.40 4.83
Mucuna 0.00 0.54 0.00
Mound
None 1.06 5.37 12.55
Poultry 0.88 4.79 12.64
Mucuna 1.06 4.85 7.43

CHAPTER
FIVE
DISCUSSION
The differences observed in particle size distribution according to the levels of degradation (Table 1)
were due to selective erosion of soil particles by runoff. The severely degraded site had lost most of
its fine particles while these were still retained more on the fairly and moderately degraded strips.
The texture of ~oil, derived from the particle size distribution, determines the potential ability of a soil
to influence crop performance. According to Wild (1993), sandy soils are light and low in nutrient
holding capacity. Ross (1989) stated further that sandy soils are porous and highly vulnerable to
leaching and run-off. Thus, sandy soils are infertile and make fertilizer use inefficient. The
implication of this is that more expenditure in terms of agricultural inputs will be required to
rehabilitate a degraded site. The coefficients of variation for particle size distribution showed that
fine particles (silt + clay) would play a critical role in response of these soils to management
practices as they varied more than sand. More variation was observed under WAS varieties
compared with ITA varieties, suggesting that varieties might have influenced changes in particle size
distribution through differences in canopy coverage of the ground.
Tropical upland soils are inherently low in soil organic matter with usually less than 50 glkg
(David et ai, 1993). The low values of organic matter (Table 1) suggested that the soil, which was
inherenijy low in soil organic matter, was depleted more at various levels of degradation, with the
trend observed from the fairly degraded to the severely degraded strips. Soil extractable P varies
widely in soils of the tropics because of the capacity of tropical soils to fix P and varying capacity of
.crops for P (Sanchez et aI., 1983). The variation in P contents at the various levels of degradation
can be attributed to differences in particle size distribution, particularly the high variations in fine
particles (Tables 1 and 2), and variation in nutrient uptake of the rice varieties.
30

There was no significant difference in the soil particles fraction in the two tillage practices (flat
and mound), though little variability was observed in the flat tillage practice having a little higher amount
of silt and mound tillage practice having a little higher amount of clay (Table 7). The higher sand is a
characteristic of the gravelly alfisols in southwestern Nigeria (FDALR, 1990; Salako et ai, 1999, 2002).
The low content of clay and silt showed high depletion of fine materials by soil erosion. With this low
clay content the field would below in cations exchange capacity as well as structural stability. It would
however appear that surface soils of alfisol in southwestern Nigeria are generally high in sand content
(Salako and Hauser, 2001).
The pH of the site being weakly acidic pointed out that the experimental site is low in cations
(Table 8). The low pH and organic matter were probably due to the continuous cropping of the soils and
insufficient recycling of plant and nutrients (Okeleye and Adetunji, 1998).
The chemical degradation has depleted much of the topsoil cations and the soil is being rendered
acidic. According to David et al (1989), organic matter of tropical soils is dynamic due to climatic
changes, which causes forming and disruption of soil aggregates. Particle size distribution of the surface
soil was similar for the three fertility management treatments. These chemical properties indicate the
inherent low fertility status of the soil due to the presence of low activity clay (Lal, 1992).
The coefficient of variation were less than 10% in all the parameters put into consideration except in
clay content of the soil having high coefficient of variability which was as high as 53%. This level of
variability in clay indicates that soil management for the replenishment of the exchangeable cations will
be very difficult.

CHAPTER
SIX
CONCLUSION
In this study, soil chemical properties of previously degraded sites planted to rice and maize were
studied. Soil degradation process was by soil erosion on rice field while it was by soil compaction on the
maize field. The least eroded site on the rice field maintained better chemical properties than the
severely degraded. However, soil chemical properties varied widely on the previously eroded sites.
Previous tillage practices caused no significant changes in soil chemical properties as observed on the
previously
eroded site.

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APPENDIX 1
RESULT OF SOIL ANALYSIS
RICE PLOT
PLOT % % % pH % % ppm cmol/kg cmol/kg cmol/kg cmol/kg H+
NO. Sand Silt Clay O.C O.M Av.P Na Ca K Mg
1 75.8 19.4 4.8 5.70 2.00 3.45 2.29 0.10 2.6 0.25 0.65 0.095
2 77.6 18.2 4.2 5.90 2.20 3.80 2.27 0.10 2.8 0.25 0.64 0.091
3 80.8 17.4 2.8 5.80 3.20 5.52 2.29 0.11 2.7 0.19 0.54 0.090
4 83.2 14.0 2.8 5.30 2.62 4.52 1.85 0.09 2.8 0.19 0.44 0.091
5 83.8 12.4 3.8 5.40 1.62 2.79 2.20 0.10 3.0 0.20 0.71 0.085
6 83.8 11.4 4.8 5.72 1.60 2.76 2.41 0.11 2.9 0.18 0.53 0.085
7 84.6 11.2 4.2 5.80 0.86 1.48 1.96 0.15 2.9 0.18 0.53 0.085
8 84.2 13.0 2.8 5.70 1.60 2.76 1.86 0.18 2.9 0.20 0.44 0.085
9 83.8 13.4 2.8 5.85 1.20 2.07 2.87 0.28 2.6 0.19 0.61 0.080
10 81.8 15.4 2.8 5.90 3.24 5.60 3.12 0.18 4.8 0.21 0.83 0.075
11 77.2 20.0 2.8 5.80 2.62 4.52 2.32 0.15 2.9 0.23 0.64 0.095
12 78.6 . 18.8 2.6 5.80 3.26 5.62 . 2.24 0.18 3.11 0.25 0.65 0.091
13 80.4 17.0 2.6 5.85 2.80 4.83 1.95 0.11 2.72 0.20 0.54 0.090
14 81.8 16.0 2.2 5.70 1.25 2.16 2.20 0.10 2.80 0.19 0.44 0.090
15 83.6 13.8 2.6 5.72 1.42 2.45 2.27 0.11 2.95 0.20 0.54 0.085
16 83.8 13.6 2.6 5.71 2.14 4.23 2.39 0.11 2.90 0.19 0.53 0.085
. .
17 84.2 12.6 3.2 5.60 1.42 2.45 2.16 0.15 2.67 0.17 0.52 0.085
18 81.8 15.4 2.8 5.30 2.22 3.83 1.90 0.15 2.74 0.19 0.54 0.091
19 82.8 14.4 2.8 5.20 2.40 4.14 2.85 0.26 2.60 0.21 0.61 0.090
20 84.6 12.2 3.2 5.80 2.82 4.86 2.96 0.24 3.40 0.23 0.52 0.090

21 82.8 14.4 2.8 5.90 3.82 6.59 3.14 0.19 4.75 0.21 0.83 0.080
22 81.4 15.8 2.8 5.80 4.24 7.31 1.95 0.35 4.21 0.23 0.81 0.075
23 83.8 13.4 2.8 5.80 4.20 7.25 2.10 0.36 4.12 0.23 0.81 0.075
24 82.6 15.2 2.2 5.65 3.82 6.59 2.05 0.11 2.86 0.21 0.54 0.080
25 82.8 14.4 2.8 5.70 4.56 7.87 2.39 0.11 4.91 0.16 0.75 0.075
26 85.8 11.4 2.8 5.70 4.20 7.25 2.27 0.10 4.90 0.16 0.75 0.075
27 86.6 10.8 2.6 5.60 3.80 6.56 2.20 0.11 3.20 0.19 0.65 0.080
28 87.8 11.4 0.8 5.85 1.24 2.14 2.06 0.15 2.52 0.16 0.73 0.075
29 86.8 12.4 0.8 5.80 0.48 0.83 1.90 0.11 2.96 0.21 0.54 0.080
30 80.6 16.6 2.8 5.75 1.50 2.59 2.18 0.10 2.65 0.23 0.82 0.080
31 81.8 15.6 2.6 5.80 2.24 3.86 2.90 0.22 2.40 0.21 0.61 0.080
32 82.8 15.0 2.2 5.75 2.20 3.80 2.20 0.10 2.60 0.23 0.83 0.075
33 79.6 ·17.8 2.6 5.70 3.82 6.60 1.80 0.15 3.80 0.19 0.80 0.075
34 80.2 17.0 2.8 5.65 3.40 5.87 1.96 0.11 3.60 0.19 0.75 0.080
35 80.8 16.4 2.8 5.71 3.16 5.45 2.00 0.15 2.65 0.21 0.61 0.075
36 82.4 15.8 1.8 5.70 3.26 5.62 2.11 0.15 4.20 0.17 0.70 0.075
37 81.6 17.2 1.2 5.75 3.40 5.87 2.17 0.11 4.25 0.19 0.75 0.080
38 84.4 14.4 1.2 5.80 2.62 4.52 2.26 0.15 3.40 0.19 0.65 0.075
39 81.8 17.4 0.8 5.60 0.68 1.173 2.12 0.16 2.50 0.16 0.73 0.075
40 80.6 18.2 1.2 5.65 0.72 1.24 1.80 0.11 2.70 0.23 0.54 0.080
41 80.4 16.8 2.8 5.75 1.20 2.07 2.16 0.10 2.60 .0.23 0.82 0.080
42 81.2 16.2 2.6 5.70 2.16 3.73 2.40 0.10 2.40 0.21 0.82 0.080
43 81.6 16.0 2.4 5.75 1.50 2.59 2.26 0.10 3.00 0.23 0.83 0.080
44 78.4 18.8 2.8 5.30 1.84 3.17 2.41 0.11 3.12 0.17 0.41 0.085

45 80.6 16.6 2.8 5.40 2.96 5.11 2.38 0.11 2.61 0.17 0.41 0.085
46 81.4 17.8 0.8 5.60 3.40 5.87 1.80 0.09 2.70 0.21 0.61 0.080
47 83.8 15.4 0.8 5.50 3.20 5.52 1.62 0.10 3.21 0.17 0.40 0.085
48 84.4 14.8 0.8 5.65 1.36 2.35 1.80 0.11 3.40 0.19 0.44 0.080
49 83.6 15.2 1.2 5.40 0.86 1.48 2.10 0.12 2.80 0.19 0.42 0.080
50 80.4 19.0 0.6 . 5.50 0.48 0.83 2.16 0.11 2.60 0.17 0.40 0.091
51 80.6 18.6 0.8 5.50 2.00 3.45 2.06 0.09 4.10 0.12 0.32 0.090
52 80.4 19.0 0.6 5.60 2.40 4.14 2.40 0.07 2.64 0.17 0.44 0.085
53 80.8 18.4 0.8 5.65 2.20 3.76 2.20 0.09 2.80 0.21 0.44 0.090
. 54 81.4 18.0 0.6 5.50 2.46 4.24 2.41 0.07 2.64 0.17 0.44 0.085
55 80.4 19.0 0.6 5.70 2.82 4.86 2.20 0.10 2.85 0.21 0.61 0.091
56 82.4 16.8 0.8 5.71 3.26 5.62 2.15 0.11 2.82 0.19 0.56 0.090
57 84.6 14.6 0.8 5.65 3.20 5.52 1.80 0.11 2.71 0.21 0.61 0.080
58 84.8 14.4 0.8 5.50 3.42 5.90 1.60 0.10 3.20 0.17 0.40 0.085
59 85.8 13.4 0.8 5.40 2.64 4.55 1.80 0.11 3.22 0.19 0.44 0.091
60 87.8 11.0 1.2 5.50 1.96 3.38 1.96 0.10 3.80 0.20 0.42 0.090
61 86.8 12.4 0.8 5.60 2.20 3.76 2.08 0.09 4.10 0.12 0.32 0.090
62 85.6 13.8 0.6 5.40 2.84 4.90 2.00 0.09 3.60 0.15 0.32 0.085
63 84.2 .15.0 0.8 5.50 2.62 4.52 2.39 0.07 2.64 0.17 0.44 0.085
64 84.6 14.4 1.2 5.65 2.60 4.49 1.86 0.07 2.70 0.19 0.80 0.091
65 85.6 13.6 0.8 5.60 2.48 4.28 2.41 0.07 2.64 0.17 0.44 0.085
66 83.8 13.4 2.8 5.30 4.00 6.90 1.81 0.07 4.11 0.51 0.95 0.080
67 85.8 11.6 2.6 5.30 4.26 7.35 1.85 0.07 4.10 0.51 0.95 0.080
68 86.6 10.8 2.6 5.40 2.20 3.76 1.80 0.07 4.20 0.17 0.75 0.080

69 85.4 12.4 2.2 5.50 2.46 4.24 1.92 0.07 3.80 0.16 0.73 0.090
70 87.8 11.4 0.8 5.30 1.62 2.80 1.72 0.07 3.75 0.21 0.80 0.085
71 87.6 11.8 0.6 5.40 1.58 2.73 1.70 0.07 3.60 0.20 0.81 0.080
72 87.8 11.4 0.8 5.65 1.52 2.62 1.75 0.07 3.75 0.21 0.80 0.085

APPENDIX 2.
RESULT OF SOIL ANALYSIS
MAIZE PLQT
PLOT % % % pH % % Av. P
SIN SAND SILT CLAY O.C O.M (ppm)
1 87.0 12.2 0.8 5.72 2.06 3.55 3.42
2 86.8 12.6 0.6 5.75 2.10 3.62 3.20
3 87.4 11.8 0.8 5.72 2.02 3.48 3.45
4 86.6 12.0 1.4 5.71 2.12 3.66 2.48
9 87.0 12.0 1.0 5.75 2.04 3.52 3.42
12 86.8 11.8 1.4 5.71 2.14 3.69 2.46
13 86.8 11.6 1.6 5.65 2.30 3.97 2.52
16 87.4 11.8 0.8 5.72 2.08 3.59 3.20
17 87.2 11.8 1.0 5.75 2.06 3.55 2.86
18 88.0 10.6 1.4 5.71 2.14 3.69 2.48
29 86.6 12.6 0.8 5.75 2.02 3.48 2.92
30 87.0 12.4 0.6 5.72 2.04 3.52 2.60
31 87.4 11.6 1.0 5.70 2.10 3.62 3.22
32 86.8 11.6 1.6 5.65 2.16 3.73 2.62
33 86.6 11.6 1.8 5.60 2.10 3.62 2.48
34 88.6 10.2 1.2 5.60 t.26 3.90 2.52
35 88.4 10.2 1.4 5.65 2.32 4.00 2.50
36 87.2 12.0 0.8 5.72 2.12 3.66 3.20
37 86.8 12.2 1.0 5.70 2.14 3.69 2.80

38 87.4 11.2 1.4 5.71 2.20 3.80 2.88
39 87.8 10.8 1.4 5.65 2.18 3.76 2.52
40 88.2 10.6 1.2 5.60 2.28 3.99 2.42

38 87.4 11.2 1.4 5.71 2.20 3.80 2.88
39 87.8 10.8 1.4 5.65 2.18 3.76 2.52
40 88.2 10.6 1.2 5.60 2.28 3.99 2.42